Downregulation of tumor necrosis factor (TNF)-α-inducible matrix metalloproteinase (MMP)-3 and MMP-13 RNA expression by mithramycin. Human SW1353 condrosarcoma cells (a), primary human femoral head chondrocytes (b) and bovine chondrocytes (c) were pre-exposed to the indicated concentrations of mithramycin for 30 min, followed by additional treatment with TNF-α for 24 hours. The MMP-3, MMP-13 and 28S RNA levels were measured by Northern hybridization, and MMP-3 protein levels were measured by Western blot analysis. For protein gels, 3 μg (a) or 4 μg (b) of protein was applied to each lane. The resulting autoradiograms indicating the respective products are shown.